1. Field of the Invention
This disclosure is generally related to bushings, and more particularly to bushings suitable to cold-expansion.
2. Description of the Related Art
There are a large number of applications where two or more parts must be joined. In many instances, the parts include apertures which must be aligned within some acceptable tolerance in order to join the parts, for example, using structure such as a pin received through the apertures. However, when the parts are assembled, the apertures may be misaligned with respect to one another for any of a variety of reasons.
One example of this problem is the assembly of a commercial airliner. The components of a commercial airliner are typically manufactured at a large number of different sites in a variety of different countries. The components may be assembled into subassemblies at these sites, or at other sites. The components and/or subassemblies are assembled into a final product at a site that is typically different from the site at which the components and/or subassemblies were produced. Thus, for example, a vertical fin or stabilizer may be manufactured at a first location, while a section of the body of the aircraft to which the vertical stabilizer will be attached is manufactured at a second location. The coupling of the vertical stabilizer to the section of the aircraft may occur at a third location.
The assembly or coupling may require an exceptionally high degree of tolerance or fit to meet the pertinent engineering specifications. This is a particular problem, for example, where the parts are manufactured at different locations. For example, environmental factors such as temperature and/or humidity may vary from location to location. Thus, a part manufactured within a defined tolerance at one location, may be out of tolerance when transported to another location. Additionally, or alternatively, parts manufactured to the same specifications at two different locations may not fit together. Even where the parts are manufactured within defined tolerances, the dimensional variations that are within the acceptable tolerance may add up (i.e., tolerance stack-up) when the parts are assembled. Since the parts are at different locations, it may not be possible to check the fit until final assembly. Even the fact that different sets of measurement tools will be employed at the different sites may hinder a successful assembly.
One approach to sizing apertures includes inserting a bushing into the aperture, securing the bushing in the aperture via cold expansion of the bushing. An expansion tool is used to exert a radially outwardly directed force to create a tight interference fit between the bushing and a sidewall of the aperture. A reaming or other machining operation is typically performed on the bushing to bring the aperture of the bushing within a desired tolerance.
The alignment problem discussed above may be further exacerbated where parts or attachment points follow a contour. Such is the situation with a set of lugs on the vertical stabilizer and the corresponding set of lugs found on the section of the aircraft to which the stabilizer is attached. The lugs of both sets generally follow the contour or camber associated with an airfoil such as the vertical stabilizer.
Present bushing-based approaches fail to adequately address the misalignment problem discussed above. A standard, inexpensive approach to addressing misalignment problems that employs a minimum number of parts would be highly desirable.